Thermostatic switch

ABSTRACT

A thermostatic switch having an L-shaped metal base attached to a header which closes one end of a metal housing. Supported from the base, and insulated from it, is a cantilever-mounted bimetal switch blade carrying a mobile contact on its free end for engagement with a stationary contact on the base. A main heater extends between a terminal carried by the header and the mounted end of the bimetal switch blade at the latter&#39;&#39;s low expansion side. An auxiliary heater extends between the base and another terminal carried by the header at the high-expansion side of the switch blade. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.

United States Patent [72] Inventor Paul R. Lee

Mansfield, Ohio [211 App]. No. 865,792 [22] Filed Oct. 13, 1969 [45]Patented Sept. 28, 1971 [73] Assignee Essex International, Inc.

[54] THERMOSTATIC SWITCH 7 Claims, 5 Drawing Figs.

[52] US. Cl 337/102, 337/112,337/113 [51] lnt.Cl ..H0lh 61/02 [50] Fieldof Search. 337/102,

[56] References Cited UNITED STATES PATENTS 2,264,988 12/1941 Lee337/366 2,820,870 1/1958 Moksu.. 337/368 3,004,203 10/1961 I Epstein337/105 X 3,194,924 7/1965 Moksu et a1. 337/113 X PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-F.' E. BellAttorney-Woodling, Krost. Granger and Rust ABSTRACT: A thermostaticswitch having an L-shaped metal base attached to a header which closesone end of a metal housing. Supported from the base, and insulated fromit. is a cantilever-mounted bimetal switch blade carrying a mobilecontact on its free end for engagement with a stationary contact on thebase. A main heater extends between a terminal carried by the header andthe mounted end of the beimetal switch blade at the latters lowexpansion side. An auxiliary heater extends between the base and anotherterminal carried by the header at the high-expansion side of the switchblade. The foregoing abstract is merely a resume of one generalapplication, is not a complete discussion of all principles of operationor applications, and is not to be construed as a limitation on the scopeof the claimed subject matter.

THERMOSTATIC SWITCH This invention relates to a thermostatic switchwhich is particularly useful in a motor protector circuit, and may beburied in the motor windings to. receive heat therefrom.

A principal object of this invention is to provide a novel and improvedthennostatic switch of high-current capacity for its physical size.

Another object of this invention is to provide such a switch which maybe tested and adjusted for its electrical and temperature-responsivecharacteristics before being encapsulated in a hermetically sealedenclosure.

Another object of this invention is to provide such a switch which maybe assembled in a convenient manner and which is rugged and durable inoperation.

Further objects and advantages of this invention will be apparent fromthe following detailed description of a presently preferred embodimentshown in the accompanying drawings, in which:

FIG. 1 is a longitudinal elevational view, with part broken away forclarity, showing the operating parts of the present switch;

FIG. 2 is a longitudinal section taken along the line 2-2 in FIG. 1 andshowing additionally the lead-in wires and parts of the switch enclosurewhich are omitted in FIG. 1 for clarity;

FIG. 3 is a perspectiveview, partly broken away for clarity, showing thesubassembly of the bimetal switchblade and the main heater in thepresent switch;

FIG. 4 is a longitudinal elevational view showing the subas sembly ofthe switch base, assembly rivet, stationary contact, header and headerterminals in the present switch; and

FIG. 5 is an elevational view of the FIG. 4 subassembly, taken from theleft end of FIG. 4.

Referring first to FIG. 1, the present switch preferably is disposedwithin a housing or body of suitable metal, preferably steel, which isclosed at its left end in this figure. The opposite end of the housing10 is closed and sealed by a metal header 11 which carries tenninals forconnecting the switch within the housing to lead-in wires. In theparticular embodiment illustrated, this header Il carries three suchterminals 12, 13 and 14, which are spaced apart laterally, as shown inFIG. 2. Terminal 12 is spot welded to the outer side of the header 1 l.Terminals 13 and 14 extend through the header at conventional glassseals (not shown) which electrically insulate them from the header 11.The outer ends of terminals 12, 13, 14, are connected throughconventional wire splices 15, I6, 17 (FIG. 2) to individual lead wires18, 19 and 20.

A sleeve 21 of suitable dielectric material extends from the header 11to the right in FIG. 2, and a suitable potting compound 22, preferableepoxy resin, fills this sleeve to anchor in place the splices 15, 16 and17. The entire assembly of the housing 10, header 11 and sleeve 21 isenclosed by a tube 23 (FIG. 2) of heat shrinkable plastic.

Inside the housing 10 the switch assembly includes a generally L-shapedsteel base having a short transverse leg 24, which is spot welded to theinner face of the header 11, and an elongated leg 25 extendingperpendicularly away from the header toward the closed end of thehousing 10. This base 24, 25 provides a rigid physical support for themovable operating parts of the switch. The header 11 conductivelyconnects the switch base 24, 25 and the switch housing 10 throughterminal 12 to the lead wire 18, which is grounded. Consequently, boththe switch base 24, 25 and the housing 10 are grounded. The header 11also supports the switch base 24, 25 spaced from direct contact with thehousing 10.

A stationary contact 26 is spot welded to the elongated leg 25 of theswitch base. To the right of this contact in the drawings the upstandingshort leg 24 of the switch base is bifurcated, as best seen in FIG. 5,presenting laterally spaced upstanding segments 24a and 24b which arespot welded at 27, 28 and 29 to the inside of the header 11.

The inner ends of the terminals 13 and 14 support an electricalinsulation panel 52 just inward from the upstanding transverse leg 24 ofthe switch base which is attached to the header ll.

At its left end in the FIGS. 1 and 2, the long leg 25 of the switch basepresents an upwardly offset boss 30 at one corner. At a location spaceddirectly behind this boss in FIGS. 1 and 2, an assembly rivet 31 is spotwelded to the switch base. This rivet has a large cylindrical lower endand a reduced diameter stem 31a extending up from the lower end. Thisstem portion of the rivet snugly receives a steel bushing 32, which hasa transversely-enlarged lower end 32a resting directly on top of thelower end of the rivet. Stacked in succession on top of the enlargedlower end 324 of bushing 32 and extending around its smaller diametershank are a mica washer 33, a porcelain washer 34, a mica washer 35, anda steel washer 36.

A unitary subassembly of a main heater 37 and a snap-acting, bimetallicswitchblade or contact carrier 38 (FIG. 3) is mounted on the rivet,bushing and washer assembly just described. The main heater 37 and thebimetal switchblade 38 are spot welded to each other at a location 39(FIG. 3) near their respective left ends in FIGS. 1 and 3. Just to theright of this location the main heater and the switchblade haverespective aligned openings 40 and 41 which snugly the porcelain washer34, as shown in FIG. 1. The attached end of the main heater 37 and theswitchblade 38 subassembly is sandwiched between the mica washers 35 and33, as shown in FIG. 1, so as to be electrically insulated from thebushing 32, the rivet 31 I and the switch base 24, 25.

The main heater 37 is a relatively thick and wide plate which isinclined upward to the right in FIGS. 1 and 3 and is in heat-transferrelationship to the switchblade 38 throughout the latters length. At itsright end the main heater is downwardly offset to present an end segment42 which is spot welded to the innner end of lead-in terminal 13 (FIG.1).

The bimetal switchblade 38 has a togglelike, overcenter springcharacteristic. As best seen in FIG. 3, it comprises a pair of outerlegs 43, 44 and a center leg 45 which is separated from the outer legsby elongated slits 46 and 47. The outer legs and the center leg of theswitchblade are integrally joined at the outer free end of the blade, aswell as at its mounted inner end. A mobile switch contact 48 is attachedto the underside of the switchblade at its outer end. In FIGS. I and 3,the top of the bimetal switchblade 38 is the low thermal expansion side,and the bottom is the high thermal-expansion side.

The outer legs 43 and 44 of the switchblade are crimped to put themunder tension and to put the center leg 45 under compression. As shownin FIG. 1, when the bimetal switchblade 38 is at a temperature below apredetermined value, it assumes an overcenter position in which its freeend is displaced downward from its mounted end, so that the mobilecontact 48 on its free end is held resiliently in engagement with thestationary contact 26, as shown in FIG. 1. When heated above thispredetermined temperature, the free end of the switchblade movesovercenter with an abrupt snap action to a position in which it holdsthe mobile contact up away from engagement with the stationary contact.Then, when the temperature drops a substantial amount below the value atwhich the contacts opened, the bimetal switchblade 38 returns overcenterwith a snap action to the F IG. 1 position, reclosing the contacts.

In the particular embodiment illustrated, the switch has an auxiliary orstarting heater 50 disposed between the switch base 25 and the bimetalswitchblade 38. This starting heater is a rodlike member which is spotwelded at one end to the raised boss 30 on the switch base 25 and isspot welded at its opposite end to the inner end of terminal 14, asshown in FIGS. 1 and 2. The auxiliary heater is in heat transferrelationship to the switchblade 38.

A flexible sheet 51 of mica or other suitable dielectric materialextends from the header 11 into the housing 10 overlying the main heater37 and the switchblade 38 to electrically insulate them from the housing10.

In the operation of this switch, the current path through the startingheater 50 is via lead-in cable 20, terminal 14, heater 50, switch base25, 24, header 11, and grounded terminal 12. The current path throughthe main heater 37 is via lead-in cable 19, terminal 13, the main heater37, switchblade 38, the normally closed switch contacts 48, 26, switchbase 25, 24, header l1 and grounded terminal 12. When the currentthrough the main heater 37 is sufficiently high, its heating effect willcause the bimetal switchblade 38, to move over center with a snap actionto separate the switch contacts 48, 26, thereby opening the circuit forthe main heater current.

A particular advantage of the present switch resides in the novel andconvenient manner in which it may be assembled. The preferred assemblysequence is as follows:

1. The mobile switch contact 48 is spot welded to the bimetalswitchblade 38;

2. The assembly rivet 31 is spot welded to the switch base 24, 25 andthen this subassembly is nickel plated;

3. The stationary contact 26 is spot welded to the switch base 24, 25.

4. The ground terminal I2 is spot welded to the header 11, which has theterminals 13 and 14 held in place by glass seals;

5. The short upstanding legs 24a and 24b of the switch base are spotwelded to the inside face of the header 11 at 27, 28 and 29, as shown inFIG. 5, to complete the subassembly shown in FIG. 4;

6. After the dielectric panel 52 is inserted over the inner ends ofterminals 13 and 14, the auxiliary heater 50 is spot welded to theterminal 14 and to the raised boss 30 on the switch base;

7. The main heater 37 is spot welded at 39 to the bimetal switchblade 38to provide the subassembly shown in FIG. 3;

8. The mica washer 33, 35, porcelain washer 34, steel washer 36 andsteel bushing 32 are stacked and riveted to the FIG. 3 subassembly;

9. The outer legs 43, 44 of the bimetal switchblade 38 are crimped, andthen the switchblade is aged at an elevated temperature;

10. The main heater and switchblade subassembly resulting from step (9)is riveted to the subassembly of the switch base, auxiliary heater,assembly rivet, bushing, washers and header which resulted from step(8);

11. The switch is temperature calibrated by bending the switch base atapproximately the location B in FIGS. 1 and 4, so that the switchcontacts 48, 26 will open at a predetermined temperature, e.g. about 240F.;

12. The offset end 42 of the main heater 37 is spot welded to the headerterminal l3;

l3. The flexible dielectric sheet 51 is positioned overlying theoperating parts of the switch and abutting at its right end against theheader, and then the housing 10 is slid over the switch assembly untilit engages the header 11, to which it is then welded to provide ahermetic seal;

14. A predetermined current is applied to terminals 13 and 14 to testthe contact opening action of the switch.

l5. The lead wires 18-20 are attached to the header terminals 12-14;

16. The header sleeve 21 is positioned against the outer side of theheader, as shown in FIG. 2, and then it is filled with the epoxy resin22;

17. The heat shrinkable tube 23 is applied over the outside of theassembly and then it is heated to shrink in place.

From the foregoing, it will be apparent that the present switch may becalibrated (by bending the switch base 24, 25)

' before it is enclosed and sealed. No manufacturing operations need beperformed on the bimetal switchblade 38 after it has been heat treated,thereby avoiding any possibility of shifting its temperature response.The mobile contact 48 is located on the switchblade 38 beyond the regionof its togglelike, overcenter snap action, so that no undesirablestresses are introduced by spot welding this contact to the switchbladeBecause the mounted end of the bimetal switchblade 38 is electricallyinsulated from the switch base 24, 25 (by washers 33, 34 and 35), themain heater 37 may be spot welded directly to this end of theswitchblade without introducing undesirable stresses.

The provision of the starting or auxiliary heater 50 at thehigh-expansion side of the bimetal switchblade 38 and the main heater 37at the low expansion side minimizes any creep action of the bimetal. Forcertain applications, however, where a slower contact-opening action ofthe switch is permissible, the starting heater 50 and its headerterminal 14 and lead-in wire 20 may be omitted.

The present switch is extremely compact in size for its currentcapacity, as well as being relatively simple to assemble, as described.This physical compactness of the switch is due in part to the novelmanner in which the main heater 37 and the bimetal switchblade 38 aremounted so as to be electrically in sulated from the switch base, withthe current flow between these elements and the switch base taking placeonly through the switch contacts.

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of the circuit and the combination andarrangement of circuit elements may be resorted to without departingfrom the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. A thermostatic switch comprising a rigid metal base,

a stationary contact supported by and conductively connected to saidbase,

an electrically conductive cantilever-mounted mobile contact carriercarrying a mobile contact on its free end in confronting relationship tosaid stationary contact,

an electrically conductive heater engaging the mounted end of the mobilecontact carrier,

support means attaching the mounted end of the mobile contact carrier tothe base and electrically insulating the mobile contact carrier from thebase,

a pair of terminals connected respectively to the base and to the heaterremote from the latters engagement with the mounted end of the mobilecontact carrier,

a metal housing receiving said base, contacts, contact carrier, heaterand support,

an electrically conductive header closing one end of said housing andhermetically sealed thereto and supporting said terminals,

said base at one end thereof having a transverse leg attached to saidheader, and

said header supports said base spaced from said housing.

2. A switch according to claim 1, wherein said support for the mobilecontact carrier is at the opposite end of the base from said transverseleg.

3. A switch according to claim 2, wherein said stationary contact islocated along the base between said support for the mobile contactcarrier and said transverse leg of the base.

4. A thermostatic switch comprising a metal housing closed at one end,

a rigid metal header closing the opposite end of said housing andhermetically sealed thereto,

a rigid metal base attached to said header and extending transverselytherefrom lengthwise into said housing in spaced relationship to thehousing,

a cantilever-mounted movable contact carrier extending generallylengthwise of the housing and having a free end,

a support assembly attached to the base and providing a cantileversupport for the opposite end of the contact carrier,

said support assembly electrically insulating the mounted end of thecontact carrier from the base,

a stationary contact mounted on the base adjacent the free end of thecontact carrier and connected conductively to the base,

a mobile contact on the free end of the contact carrier for engagementwith the stationary contact,

a terminal projecting through the header into the interior of thehousing, and

comprising an additional terminal extending through the header, and anauxiliary heater connected at one end to the inner end of saidadditional terminal and at its opposite end to the base,

said auxiliary heater being disposed between switchblade and the base.

7. A thermostatic switch according to claim 4, wherein said metal basemay be bent transversely to its lengthwise dimension to calibrate thetemperature of actuation of said contacts.

the

1. A thermostatic switch comprising a rigid metal base, a stationarycontact supported by and conductively connected to said base, anelectrically conductive cantilever-mounted mobile contact carriercarrying a mobile contact on its free end in confronting relationship tosaid stationary contact, an electrically conductive heater engaging themounted end of the mobile contact carrier, support means attaching themounted end of the mobile contact carrier to the base and electricallyinsulating the mobile contact carrier from the base, a pair of terminalsconnected resPectively to the base and to the heater remote from thelatter''s engagement with the mounted end of the mobile contact carrier,a metal housing receiving said base, contacts, contact carrier, heaterand support, an electrically conductive header closing one end of saidhousing and hermetically sealed thereto and supporting said terminals,said base at one end thereof having a transverse leg attached to saidheader, and said header supports said base spaced from said housing. 2.A switch according to claim 1, wherein said support for the mobilecontact carrier is at the opposite end of the base from said transverseleg.
 3. A switch according to claim 2, wherein said stationary contactis located along the base between said support for the mobile contactcarrier and said transverse leg of the base.
 4. A thermostatic switchcomprising a metal housing closed at one end, a rigid metal headerclosing the opposite end of said housing and hermetically sealedthereto, a rigid metal base attached to said header and extendingtransversely therefrom lengthwise into said housing in spacedrelationship to the housing, a cantilever-mounted movable contactcarrier extending generally lengthwise of the housing and having a freeend, a support assembly attached to the base and providing a cantileversupport for the opposite end of the contact carrier, said supportassembly electrically insulating the mounted end of the contact carrierfrom the base, a stationary contact mounted on the base adjacent thefree end of the contact carrier and connected conductively to the base,a mobile contact on the free end of the contact carrier for engagementwith the stationary contact, a terminal projecting through the headerinto the interior of the housing, and a heater connected at one end tosaid terminal and at its opposite end to the cantilever-mounted end ofthe contact carrier.
 5. A thermostatic switch according to claim 4,wherein said contact carrier is a snap-acting bimetal switchblade havinga high expansion side facing toward the base and a low expansion sidefacing away from the base, and said heater is disposed at the lowexpansion side of the switchblade.
 6. A thermostatic switch according toclaim 5, and further comprising an additional terminal extending throughthe header, and an auxiliary heater connected at one end to the innerend of said additional terminal and at its opposite end to the base,said auxiliary heater being disposed between the switchblade and thebase.
 7. A thermostatic switch according to claim 4, wherein said metalbase may be bent transversely to its lengthwise dimension to calibratethe temperature of actuation of said contacts.